1. Field
The present invention relates generally to equalization in communications systems, and more specifically, to a universal receiver incorporating virtual parallel equalizers.
2. Background
Communications systems are used for transmission of information from one device to another. Prior to transmission, information is encoded into a format suitable for transmission over a communication channel. The transmitted signal is distorted as it travels through the communication channel; the signal also experiences degradation from noise and interference picked up during transmission. An example of interference commonly encountered in bandlimited channels is called inter-symbol interference (ISI). ISI occurs as a result of the spreading of a transmitted symbol pulse due to the dispersive nature of the channel, which results in an overlap of adjacent symbol pulses. The received signal is decoded and translated into the original pre-encoded form. Both the transmitter and receiver are designed to minimize the effects of channel imperfections and interference. For the purposes of this disclosure, interference or distortion due to channel imperfections, or any combination thereof will be referred to generally as noise.
Various receiver designs may be implemented to compensate for noise caused by the transmitter and the channel. By way of example, an equalizer is a common choice for dealing with ISI. An equalizer corrects for distortions and generates an estimate of the transmitted symbol. In the wireless environment, equalizers are required to handle time-varying channel conditions. Ideally, the response of the equalizer adjusts to changes in channel characteristics. The ability of the equalizer to respond to changing conditions is related to the number of taps of the equalizer. More taps allow the equalizer to more accurately adjust to changes, while fewer taps allow faster adaptation. Optimizing the equalizer by selecting the number of taps is difficult, as this requires a balancing of competing goals.
A need exists, therefore, for an equalizer design that optimizes performance for a variety of systems and conditions.